1. Field of Invention
The invention relates to an electrophotographic type image forming apparatus, such as a laser printer.
2. Description of Related Art
An image forming apparatus of an electrophotographic type includes a developing roller that holds toner thereon, a photosensitive drum, on which an electrostatic latent image is formed, an image transfer roller that is used to transfer a visible toner image onto a sheet, and a cleaning roller that cleans a surface of the photosensitive drum.
The toner held on the developing roller is supplied onto the electrostatic latent image formed on the photosensitive drum to form a visible toner image. The visible toner image is then transferred onto a sheet by the image transfer roller, and thus, an image is formed on the sheet. However, some toner may remain on the photosensitive drum after the visible toner image is transferred onto the sheet.
As a bias is applied to the cleaning roller, the toner, which remains on the photosensitive drum, is electrically captured and removed by the cleaning roller. Thus, the surface of the photosensitive drum is cleaned. Therefore, an image forming operation can be performed in an excellent condition every time.
In a case where a motor for driving the photosensitive drum and the bias for the cleaning roller are simultaneously turned on when the image forming operation starts, the photosensitive drum starts rotating before the bias is applied to the cleaning roller. In this case, the toner, which has been captured and removed by the cleaning roller at the last image forming operation, adheres again to the photosensitive drum.
Further, in a case where the motor and the bias for the cleaning roller are simultaneously turned off when the image forming operation is completed, the photosensitive drum rotates for a while due to inertia, not stopping immediately. While the photosensitive drum rotates due to inertia, the toner, which has been captured and removed by the cleaning roller, again adheres to the photosensitive drum.
In particular, when a rotational speed of the motor is set to a high speed in order to speed up the image forming operation, the photosensitive drum is apt to rotate due to inertia. Therefore, the above-described problem is brought to the fore.
Further, the readhesion of the toner onto the photosensitive drum causes distortion of images, thereby causing a deterioration in image quality.